JOHANNESBURG (CNN) — Former South African President Nelson Mandela was conscious when he was admitted to a hospital for a recurring lung infection, the president’s office said Thursday.

Mandela, 94, was admitted to the hospital just before midnight Wednesday, his second hospitalization this month.

The anti-apartheid icon and nation’s first black president has become increasingly frail over the years, and he has not appeared in public since 2010.

“Doctors are attending to him, ensuring that he has the best possible expert medical treatment and comfort,” President Jacob Zuma’s office said in a statement.

“We appeal to the people of South Africa and the world to pray for our beloved Madiba and his family, and to keep them in their thoughts.”

Madiba refers to his affectionate clan name, which is widely used in the nation.

Zuma’s office did not say what hospital he was admitted to, and he renewed calls for his privacy.

Earlier this month, the Nobel laureate was hospitalized for what officials described as a routine checkup.

Mandela has been treated for the ailment before, including a Christmas hospital stay last year when he also had gallstone surgery. He was also treated for an acute respiratory infection in 2011.

Considered the founding father of South Africa’s democracy, Mandela became an international figure when he endured 27 years in prison for fighting racial segregation.

During his imprisonment, he suffered from tuberculosis, and he has battled respiratory infections over the years.

He was freed in 1990. Three years later, he and then-South African President F.W. de Klerk won the Nobel Peace Prize.

In 1994, Mandela was elected president, serving only one term as he had promised.

Despite his rare public appearances in recent years, he retains his popularity and is considered a hero of democracy in the nation. Last year, South Africa launched a new batch of banknotes with a picture of a smiling Mandela on the front, a testament to his iconic status in the nation.

Mandela’s impact extends far beyond South African borders. After he left office in 1999, he was involved in mediating conflicts from Africa to the Mideast.